On the two points that you made, this is what he said 'Ryan Giggs played underage football for England while being Welsh', Giggs played for England at schoolboy level and he even captained them, so what how is what he said not true?
Secondly, on his other point, which you also claim is untrue, 'People from the Nationalist community in the north tend not to follow Northern Ireland and identify themselves as Irish and not Northern Irish, but because they are born north of the border at underage level they have to declare for Northern Ireland until they reach senior levels.', He is partly correct in what he is saying, and I will tell you why. If you are born in the north you are most likely playing for a local side under the IFA's jurisdiction, and therefore will be known within their system. If you are talented, you will be approached to play at schoolboy level possibly even fast tracked through the under age levels. To represent them you will need to declare for them, which most will do especially if they aspire to be professionals, and why wouldn't they do this? (but granted, this is a different debate). The FAI most likely won't know who they are yet, and won't get the chance to represent the Republic at schoolboy level due to lack of exposure to the FAI. It's a debatable point but not untrue!
So most of what he said in my opinion is spot on, maybe could have been worded a little better, but I'll stand my ground and reconfirm that I completely agree with what he said.